Selenium : webdriver did not recognized the webelement - webdriver

Question

Can any one figure out this issue
I generated the script for login page, after login i wanted to log out the app or perform some action on that current page but i failed to do so. I performed by xpath,name,id. I also put thread.sleep but system gave me such error.
Exception in thread "main" org.openqa.selenium.NoSuchElementException: Unable to locate element: {"method":"id","selector":"LnkLogoff"}
Command duration or timeout: 30.52 seconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: '2.32.0', revision: '6c40c18', time: '2013-04-09 17:23:22'
System info: os.name: 'Windows XP', os.arch: 'x86', os.version: '5.1', java.version: '1.6.0_22'
Session ID: 187840f8-dc3c-4885-ae8a-6192dae1b552
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{platform=XP, acceptSslCerts=true, javascriptEnabled=true, browserName=firefox, rotatable=false, locationContextEnabled=true, version=20.0.1, cssSelectorsEnabled=true, databaseEnabled=true, handlesAlerts=true, browserConnectionEnabled=true, nativeEvents=true, webStorageEnabled=true, applicationCacheEnabled=true, takesScreenshot=true}]
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:187)
at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:145)
at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:554)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:307)
at org.openqa.selenium.remote.RemoteWebDriver.findElementById(RemoteWebDriver.java:348)
at org.openqa.selenium.By$ById.findElement(By.java:216)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:299)
at testsuite.n2.main(n2.java:39)
Caused by: org.openqa.selenium.remote.ErrorHandler$UnknownServerException: Unable to locate element: {"method":"id","selector":"LnkLogoff"}
Build info: version: '2.32.0', revision: '6c40c18', time: '2013-04-09 17:23:22'
System info: os.name: 'Windows XP', os.arch: 'x86', os.version: '5.1', java.version: '1.6.0_22'
Driver info: driver.version: unknown
at <anonymous class>.FirefoxDriver.prototype.findElementInternal_(file:///C:/DOCUME~1/NCHAUD~1/LOCALS~1/Temp/anonymous526938929382849157webdriver-profile/extensions/fxdriver#googlecode.com/components/driver_component.js:8405)
at <anonymous class>.fxdriver.Timer.prototype.setTimeout/<.notify(file:///C:/DOCUME~1/NCHAUD~1/LOCALS~1/Temp/anonymous526938929382849157webdriver-profile/extensions/fxdriver#googlecode.com/components/driver_component.js:386)